Method for processing a cathode ray tube having improved life

ABSTRACT

A METHOD FOR PROCESSING AN IMPROVED CATHODE RAY TUBE EMPLOYING AN OPEN METALLIC STRUCTURE POSITIONED RELATIVE TO THE SCREEN, FOR EXAMPLE, A SHADOW MASK COLOR TUBE WHEREIN THE MASK IS A CONTINUOUS SELECTED GASEOUS GIVING   MECHANISM DURING TUBE OPERATION. DURING TUBE PROCESSING THE MASK SORBS A SELECTED INTRODUCED GAS SUCH AS HYDROGEN. ELECTRON BEAM IMPINGEMENT OF THE MASK DURING SUBSEQUENT TUBE OPERATION EFFECTS GRADUAL RELEASE OF THE OCCLUDED SELECTED GAS FROM THE MASK TO PROVIDE A REPLENISHABLE PARTIAL PRESSURE OF HYDROGEN WHICH IN RELATION TO THE TOTAL TUBE PRESSURE IS CONSISTENT FOR THE PROMOTION OF ENHANCED EMISSION AND EXTENDED TUBE LIFE.

D. BENDA Jan. 5, 1971 METHOD FOR PROCESSING A CATHODE RAY TUBE HAVINGIMPROVED LIFE Original Filed Nov. 1'7, 1966 0 F- MD R6 was SUM. M& P

M IM 1 T S H HS 3 5 w HM E U mm Vs E INVENTOR. DAV D BENDA ATTORNEYUnited States Patent 3,552,818 METHOD FOR PROCESSING A CATHODE RAY TUBEHAVING IMPROVED LIFE David Benda, Geneva, N.Y., assignor to SylvaniaElectric Products Inc., a corporation of Delaware Original applicationNov. 17, 1966, Ser. No. 595,104, now

Patent No. 3,432,712, dated Mar. 11, 1969. Divided and this applicationJuly 18, 1968, Ser. No. 745,812

Int. Cl. HOlj 9/38 US. Cl. 316-11 Claims ABSTRACT OF THE DISCLOSURE Amethod for processing an improved cathode ray tube employing an openmetallic structure positioned relative to the screen, for example, ashadow mask color tube wherein the mask is a continuous selected gaseousgiving mechanism during tube operation. During tube processing the masksorbs a selected introduced gas such as hydrogen. Electron beamimpingement of the mask during subsequent tube operation effects gradualrelease of the occluded selected gas from the mask to provide areplenishable partial pressure of hydrogen which in relation to thetotal tube pressure is consistent for the promotion of enhanced emissionand extended tube life.

CROSS REFERENCE TO RELATED APPLICATION This application is a divisionalapplication of SN. 595,104, filed Nov. 17, 1966 which issued as US. Pat.3,432,712 on Mar. 11, 1969, and is assigned to the assignee of thepresent invention.

BACKGROUND OF THE INVENTION This invention relates to cathode ray tubesand more particularly to a cathode ray tube employing a substantiallyopen metallic member spaced relative to the screen whereof the tube hasimproved life performance and a method for processing the tube toachieve the desired performance.

The useful operational life of electron tubes, of which cathode raytubes are an example, is dependent largely upon the level of electronemission available for utilization in the device. In color cathode raytubes, for example, one or more cathodic sources are incorporated in theelectron gun structures oriented within the conventionally evacuatedenvelope to provide a continuous supply of electrons to effect tubeoperation. These electrons substantially released by heat from thebarium compounds of the cathodes are formed or shaped into beams,focused, accelerated, and directed from the terminal end of the gunstructure toward an electron responsive screen by appropriatelyassociated gun elements. Means external of the tube are utilized todeflect the beams in a predetermined sweeping manner to provide discreteimpingement of the beams on the screen thereby producing desiredluminescent displays. Thus, the sustained generation of electrons of apredetermined level of supply is necessary to maintain prolonged tubeoperation of a desired degree.

In shadow mask cathode ray tubes of the type described, it is customaryto position a getter structure adjacent the terminal end of the gun.This getter is formed to eifuse a gas-adsorbing material, such asbarium, during a specific sequence in tube processing to dispose a thinfilm of gettering material substantially on the walls of the envelopeand on the surface of the shadow mask facing thereto. While a thin filmof gas-adsorbing barium material, having a substantially uniformthickness, is desired for optimum gas clean-up, the directionaldispersion of the gettering material in the reduced atmosphere tends to3,552,818 Patented Jan. 5, 1971 dispose a thicker and somewhat lessefficient film on predominantly the central surface area of the mask.

While degassing of the tube components is practical before and duringtube processing, additional occluded gases are released during tubeoperation from the various elemental tube structure and envelope intothe substantially evacuated interior. These gases, as for example, N 0 HC0, C0 and H 0 are for the most part effectively adsorbed by the getterfilm, but as tube life progresses getter clean-up etficiency decreases,and some of the heavier gaseous hydrocarbons, such as acetylene (C H aresometimes evidenced. These hydrocarbon ions, being attracted by thecathode, deleteriously bombard and impair the emissive surface thereof.As the supply level of electron generation decreases as a result ofcathode deterioration, a change is evidenced in the tube operatingcharacteristics. When these characteristics drop below a certainprescribed parameter, tube life is said to be affected.

It is known that the electron emission of electron tubes may bebenefited by the introduction thereinto of specific pressure of selectedgases such as, for example, nitrogen or hydrogen, but there has been noreadily feasible means for maintaining an optimum emission-promotingpartial pressure of the desired gas within the operating tube.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of this inventionto reduce the aforementioned disadvantages and to produce an improvedcathode ray tube that, when processed, has a continuous selected gaseousgiving mechanism during tube operation to enhance electron emission andpromote extended tube performance.

A further object is to produce a color cathode ray tube that hasimproved gas adsorbing capabilities.

An additional object is to provide a method for processing a colorcathode ray tube to effect means for maintaining therein an electronemission-promoting-partial pressure of a selected gas during tubeoperation to extend the life thereof.

The foregoing objects are achieved in one aspect of the invention by theprovision of a method for processing a cathode ray tube for example acolor tube employing an open metallic member, such as a shadow mask,wherein the tube is heated and substantially evacuated of occludedgases, the cathode materials converted to the electron emission state,the tube evacuation terminated, and a volume of a selected gasintroduced into the substantially evacuated tube while the masktemperature is of a level to effect selected gas sorption therein. Theselected gas, being chemically compatible with the screen and electronemission materials, is appreciably sorbed by the conditioned mask andreleased in a gradual manner therefrom by electron bombardment of themask in said subsequent 1y operating tube. Thus, there is providedtherein a replenishable partial pressure of the selected gas in relationto a total tube pressure to promote enhanced electron emission andextended tube life. Subsequent to the initial introduction of theselected gas, a layer of gas sorbing getter material is diffused overthe mask surface proximal to the electron gun; this getter materialhaving a low sorption sensitivity for the selected gas.

For a better understanding of the present invention, together with otherand further objects, advantages, and capabilities thereof, reference ismade to the following specification and appended claims in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS 3 FIG. 2 is a perspective view of onetype of material effusing structure; and

FIG. 3 is a plan view showing one embodiment for introducting theselected atmosphere in the evacuated tube.

DESCRIPTION OF THE PREFERRED EMBODIMENT For simplicity and ease ofunderstanding, while in no way limiting, the invention will be describedwith reference to a inch rectangular shadow mask color cathode ray tubehaving substantially 90 degree electron beam deflection as indicated byLot in FIG. 1. The shadow mask is but one type of open metallic member.Other structures intended to be within the scope of the inventioninclude grids, perimetric frames and other structures that are orientedrelative to the screen and can be impinged by the scanning electronbeam.

With further reference to the figures there is shown a shadow mask colorcathode ray tube 11 of the type above noted having an envelope 13integrally comprising a neck portion 15, a funnel portion 17, and apanel portion 19. A patterned cathodoluminescent screen 21 of selectedelectron responsive phosphors is formed on the inner surface of thepanel portion 19. Adjacent to the screen and spaced therefrom is theforaminous shadow mask structure 23 which comprises the supporting frame25 and the peripherally attached apertured mask 27. The mask frame isspacedly oriented within the panel by suitable support means 29.

In greater detail, the formed apertured mask portion 27 is of low carbonsteel material, such as SAE 1010 formulation or a similar material, of athickness in the order of .006 inch. The supporting frame portion 25 isof similar low carbon steel material having a nominal thickness of .093inch. The holes 26 in the apertured portion which are associated withthe screen pattern therebeneath are substantially circular in shape andrange in diametrical size from about .0110 inch at the center to about.0098 inch at the edge. While the apertured mask portion compirses amultitudinous number of these holes, the transmission of the mask is inthe order of about 16 percent at the center diminishing to about 11percent at the edge. Thus, the solid web of mask material 28 comprisesabout 84 to 89 percent of the mask area.

Extending from the mask frame is electrical connective means 31 whichmakes contact with the Aquadag coating 33 disposed on the interiorsurface of the funnel 17 and extending partially into the neck portion15.

Disposed within the neck of the tube is the electron gun mount structure35- which for clarity is only partially detailed and illustrates onlyone electron source or cathode 37. The beam covergence means 39terminally oriented on the mount has reilient support and connectivemeans 41 making pressured electrical contact with the Aquadag coatingextending into the neck portion. Spaced from and supported relativethereto by a positioner 42 extending from the covergence means is onetype of a material effusing structure 43 which will be detailed later inthis specification. The mount structure 35 is further positionallysupported on electrically conductive pins (of which only four are shown)45, 46, 47, and 48 which are hermetically sealed in the stem waferclosure portion 51 to extend interiorly and exteriorly therefrom.

An exhaust tubulation 53 is connected through appropriate valving 55 toa conventional vacuum or gas evacuation system. In the tubulation thereis noted, by dotted lines, the region of hermetic tubulation seal 57which is consummated by heat prior to removal of the tube from thevalve.

In processing, the tube 11 is oriented in a manner to expediteconnection of the exhaust tubulation 53 with the evacuation system.External heat is applied to the tube, by means not shown, tosubstantially degas the envelope 13, the screen 21, the shadow maskstructure 23, the Aquadag coating 33, and the gun mount structure 35 ofgases occluded therein. During this outgassing heating step the maskreaches a temperature in the order of 380 to 400 degrees centigrade. Theinternal ambient and released occluded gases within the tube areevacuated through the externally connceted vacuum system by extendedpumping during the heating sequences. It is conventional to supply extraheat to the electron gun mount structure 35, especially to the lowerportion thereof, by induction heating means substantially localizedrelative to the neck portion of the tube.

Additional heat is applied to the cathode 37 during at least part of thelatter sequences of the evacuation period and during at least a portionof the latter part of the tube heating period to chemically convert theemission materials 38 to an electron emitting state. For example, themajor constituent of the emission materials combination, bariumcarbonate (BaCO is converted during tube processing to barium which isthe functional electron emitter during subsequent tube operation, theemissive action of which may be augmented by including strontium andcalcium in the emissive coating. The aforementioned additional cathodeheat is supplied thereto by electrically activating the cathode heater40 which is insulatively positioned within the nickel alloy cathodesleeve 37. This heater activation is accomplished by connecting heaterpins 46 and 47 to an appropriate electrical supply source, not shown.

When degassing and evacuation have reached predetermined levels, theexternally connceted evacuation period is teminated in accordance withthe way the selected gas is to be introduced into the tube. If theselected gas 56 is supplied by a subsequently activated giver orientedwithin the tube, the evacuation termination is consummated by etfectinga tip off heat seal 57 in the exhaust tubulation. Alternatively, if theselected gas is to be supplied from an external pressurized supply asshown in FIG. 3, the valve is replaced by a twoway valving device 55which terminates the evacuation, and when desired, can be adjusted toallow a predtermined pressure of the selected gas to enter thesubstantially evacuated tube envelope, after which the valve is closedand the tubulation seal 57 effected.

At the termination of externally connected evacuation period, thetemperature of the shadow mask is approximately 200 degrees centigrade.It has been found desirable to introduce the selected gas while the masktemperature is at least degrees centigrade and preferably while it is inthe range between 100 and degrees centigrade. While the mask is coolingthrough the aforementioned temperature range, the expansive surface ofthe foraminous mask structure of degassed porous low carbon steel sorbsor getters a large amount of the selected gas. Naturally other internalcomponents of the tube sorb a certain amount of the selected gas, butthe amount is far less than that sorbed by the mask.

The term selected gas is herein used with reference to a gaseouscomposition, of one or more gases, that is chemically compatible withthe phosphors of the screen and the converted electron emissionmaterials of the cathode, and one that is not appreciably sorbed by thesubsequently applied getter material, such gases for example may behydrogen or nitrogen or an inclusive mixture. By way of example in thisinstance, hydrogen (H will be described as the selected gas of thedesired type. It has been discovered that maintenance of a predeterminedpartial pressure range of H in the subsequently operating cathode raytube enhances electron emission and improves overall tube lifeperformance.

As previously mentioned, the selected gas can be introduced in severalways. By way of example, one type of material eifusing structure 43 willbe described. This ringlike structure is of a metallic material such asnonmagnetic stainless-steel formed as an open trough or channel facingthe mask and containing at least two types of efiusing materials 44. Oneof these is a hydrogen giver as for example a hydride of a metal such aszirconium or titanium, of an amount which when heated will release thedesired volume of hydrogen; the other material is a gettering substancesuch as -BaAl from which barium is released upon heating. Although notshown, it is in keeping with the invention to utilize a separate Heifusing structure and a separate getter structure, if so desired.

When the mask is in the desired temperature range, the material etfusingstructure 43 is heated by localized induction means, not shown. As thering reaches the 500 to 600 degree centigrade temperature range,dissociation of the hydride materializes and H is released into thesubstantially evacuated interior of the tube. As previously mentioned, alarge quantity of the released H is sorbed by the conditioned mask whilethe remainder constitutes a partial pressure within the tube. Anothergas evidenced as a partial pressure at this stage of processing is argon(Ar). This inert gas, which is conventionally utilized as an ambientmedium during the storage of etfusing structures and sorbed to a limiteddegree thereby, is released by heat to contribute to theinitial totaltube pressure. During early tube life, this inert gas appears to belargely sorbed in a seemingly harmless manner by the tube componentsother than the Ba getter material. Increasing the ring temperature toapproximately 1100 degrees centigrade volatilizes the Ba getteringmaterial which is directively etfused into the partial pressures ofhydrogen and argon by the open channel shaping of the ring. The bariummolecules in contacting and colliding with the predominantly hydrogenmolecules, sorb a limited amount of the hydrogen and are beneficiallydeflected and diffused to form a layer of gas sorbing getter material ofan efficient thickness over the surface of the mask proximal to theelectron beam source. Some of the getter material is also diffusedtoward and deposited on the surface of the Aquadaged funnel portion. Thepresence of the additional partial pressure of H provides a more uniformdistribution of gettering material than is possible in a tube having alow total pressure. After flashing of the getter, the tube is highvoltage conditioned and further electrically processed in substantiallythe conventional manner.

If it is desired to introduce the H from a pressurized external sourceas aforementioned and shown in FIG. 3, the material effusing structurewould be a conventional channelized getter, formed similar to thestructure already described but containing only getter material. Afterthe H is introduced and the tube seal 57 accomplished, the conventionalgetter ring is inductively heated whereupon the Ba material isadvantageously flashed or diffused as previously described.

As an aid to further description, the cathode ray tube shown in FIG. 1will be considered as a sealed and finished tube having a hydrogenatmosphere 56 therein and operating in a typical situation, theconditions of which are not shown. The electron beam 59 emanating fromthe electron gun is appropriately deflected through the Lot to sweep thescreen, and in so doing, usually overscans the mask. Thus, the beamimpinges substantially the whole of the gettered surface of the shadowmask structure 23. In a color cathode ray tube the electron guns operateat much higher cathode currents and anode voltages than do monochromeguns; the color gun conditions being in the order of 1 ma. cathodecurrent and 25 kv. anode potential. The beam impingement on theaforedescribed expansive surface of the mask structure converts a largeportion of the electrokinetic energy of the beam into heat. The impactof the beam appears to be at least two-fold, namely the high velocityelectron impingement of the moving beam frees some of the loosely heldsorbed H from the Ba getter layer, and the heat resultant from thesequential impacts promotes continued release of occluded H from themask material proper. The mask temperature due to beam bombardment in anormally operating color tube will be substantially in the range of 55to 60 degrees centigrade.

This is substantially an equalized temperature resulting from theconduction and dissipation of the electron-mask impact heat within thematerial web of the mask effected by the rapidly scanning electron beam;whereof the momentary temperature rise at the point of impact isappreciably above 60 degrees centigrade. Thus, it has been found thatthe mask, which is processed to be literally impregnated with H becomesa continuing H giver under operational electron bombardment and the heatresultant therefrom to provide a replenishable partial pressure ofhydrogen at a rate to promote enhanced electron emission and extendedtube life.

The efficient and substantially uniform thickness of the getter layernot only provides improved gettering but also promotes uniform heatingof the mask by the beam which augments constancy of H release.

Since the low carbon steel mask and frame material exhibits a greataffinity for hydrogen, a greater partial pressure of this selected gasis introduced into the tube during processing than is evidenced in thesubsequently finished tube. The desired amount of hydrogen content hasbeen determined by extensive experimentation and observation of totaltube pressures and related partial pressures during tube life. Thus, byanalytical observations of the desired results, desired initial gaseouscontent can be calculated.

Immediately following gettering, the total tube pressure is relativelyhigh, and may be, for example, in the order of 10'- torr. At this stage,the major partial pressures contributing to the total include H Ar, C0,C0 and N During tube aging, stabilization, and testing a semblance ofgaseous equilibrium becomes evidence within the tube. For example, at avery early period in life, such as during the one to two hour period,the total gas pressure may drop to the vicinity of 10- torr, the majorportion of which is a partial pressure of H not lower than substantiallyone magnitude (9X10- below the total tube pressure. In other words, thepartial pressure of hydrogen comprises substantially ninety percent ofthe total tube pressure. This relationship is substantially maintainedduring ensuing tube life; for example, at 1000 hour life the total tubepressure may be 1X10 torr whereof the H partial pressure would not beless than substantially 9 l0- torr. Likewise, at the 5000 hour level,the range between total tube pressure and the H partial pressure wouldnot exceed substantially one magnitude. Too great a H pressure is notdesired; for optimum benefits, it should be substantially less than thetotal tube pressure but not more than substantially one magnitudetherebelow.

During tube operation, there are minor partial pressures of gasesevolved, most of which are of insignificant pressure gradients or of atype successfully gettered in accordance with the capabilities of therespective gettering materials utilized.

The reasons for the beneficial effects of the major partial H pressurein the operating tube are not fully understood. In most conventionalcolor cathode ray tubes, a minor partial H pressure, evidenced duringearly life, disappears or drops to an insignificant level as lifeprogresses. The enhanced electron emission and extended tube life areresults evidenced from the continued presence of a major partial Hpressure as furnished by the replenisher within the tube. Hydrogencontent of the pres sure values indicated appear to deter the formationof certain heavy hydrocarbons, such as ethane (C H and acetylene (C Hwhich seem to be associated with slumping emission in conventionaltubes. It is thought that the positive ions of these undesirablehydrocarbons deleteriously bombard the negatively charged emissivecathode coating. It is further thought that the presence of a majorpartial H pressure may effect a carbon combination in other than agaseous form. Whatever the chemical and electrical mechanisms involved,marked life improvement is noted when a cathode ray tube is processed ina manner that the open metallic structure becomes a continuous selectedgaseous giving mechanism during tube operation.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the scope of the inven tion as defined bythe appended claims.

I claim:

1. In the manufacture of a cathode ray tube employing within an envelopethe elemental structure of a cathodoluminescent screen, a fora-minousmetallic member spaced adjacent thereto and being of a porous materialparticularly conducive for gas sorption, and at least one source ofelectron beams employing a cathode having emission materials thereon, aprocessing procedure to effect, in the subsequently operating tube, areplenishing partial pressure of a selected gas by electron bombardmentof said foraminous member, said process comprising the steps of:

heating said tube to substantially degas said envelope and saidelemental structures of gases occluded therein;

substantially evacuating said tube of internal ambient and said releasedoccluded gases through an eX- ternally connected system;

heating said cathode to chemically convert said emission materials to anelectron emitting state, said cathode heating being effected during atleast part of said evacuation period and at least during part of saidtube heating period;

terminating said externally connected evacuation period of said tube;

introducing a predetermined volume of a selected gas into saidsubstantially evacuated tube while the temperature of said foraminousmetallic member adjacent said screen is decreasing but still at a levelto effect appreciable gas sorption, said selected gas being chemicallycompatible with said screen and said con verted emission materials, saidvolume being suflicient to provide in said subsequently operating tube areplenishable high partial pressure of said selected gas in relation toa total tube pressure to promote enhanced electron emission and extendedtube life; and

disposing a layer of active gas sorbing getter material of an eflicientthickness over the surface of said forarninous metallic member proximalto said electron beam source, said getter material having a low sorptionsensitivity for said selected gas.

2. The cathode ray tube processing procedure according to claim 1wherein said introduced selected gas is substantially hydrogen, andwherein said temperature of said foraminous metallic member is at leastdegrees centigrade when said gas is introduced.

3. The cathode ray tube processing procedure according to claim 1wherein said selected gas is introduced in a volume to provide in saidoperating tube a high partial pressure not lower than substantially onemagnitude below said total tube pressure.

4. The cathode ray tube processing procedure according to claim 1wherein at the termination of said evacuation period said tube is sealedand said selected gas is subsequently introduced by the subsequentactivation of a selective gas given priorly positioned within saidenvelope.

5. The cathode ray tube processing procedure according to claim 1wherein said selected gas is introduced from an external pressurizedsupply after which the tube is sealed prior to deposition of said gettermaterial.

References Cited UNITED STATES PATENTS 2,497,911 2/1950 Reilley et al316-1 1X 2,884,777 7/1958 Szegho 313-178X 3,108,706 10/ 1963 Matsch etal. 2060.4X 3,167,678 1/1965 Griessel 2060.4X

H. A. KILBY, JR., Primary Examiner Patent 'No. 3 ,552 ,818

Inventor 5) Dated January 5, 1971 DAVID BENDA It is certified that errorappears in the above-identified patent and that saidletters Patent arehereby corrected as shown below:

Column 3, line 53, of the specification, "covergence" shouldread--convergence--.

Column 3, line 54 "reilient" should read--resilient--.

Column 8, Claim 4, Line 25 "given" should read--giver--.

Signed and sealed this 6th day of April 1971 (SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

EDWARD M.FLET0HER,JR

Commissioner of Patents Attesting Officer

